The reports said 10 people died in the riots Tuesday and two others were shot to death by police.
CNN said the Xinhua news agency gave no details about how the riots started but said a group of knife-wielding assailants had attacked people in a market in Yecheng County.
Ethnic unrest has been simmering in the region for years, with Chinese authorities blaming Uighur militants for the violence.
The Muslim Uighurs are members of China's Turkic-speaking minority, who resent being ruled by majority Han Chinese.
China says foreign Uighur groups linked to the East Turkistan Islamic Movement is to blame for the trouble in the region. Chinese authorities have said the movement trains in neighboring Pakistan, a close ally of China.
Last December, officials in Xinjiang-Uighur said police shot and killed seven people in an alleged kidnap-hostage case, in which one officer also died. The World Uighur Congress, based in Stockholm, disputed the allegations, saying the victims died when police fired on demonstrators protesting a recent crackdown.
In July 2009, about 200 people died in Urumqi, capital of Xinjiang-Uighur. Since then, China has increased its government surveillance and police actions, triggering more resentment among the Uighurs.